LD Side Pumped Er³⁺,Yb³⁺:Glass Waveguide Passively Q-switched Laser

LD pumped Er³⁺,Yb³⁺:glass laser is a common way to obtain 1.5μm wavelength safe laser output because of its small size,compact and simple structure,high reliability and high overall efficiency.The 1.5μm short pulse laser with high energy and narrow pulse width has urgent applications in military and civil fields.This thesis focuses on the research progress of 1.5μm laser output at home and abroad,and researches on the LD pumped Er³⁺,Yb³⁺:glass directly output 1.5μm laser.The latest research results of LD pumped Er³⁺,Yb³⁺:glass are compared and analyzed comprehensively.Passive Q-switching using the saturable absorption property of cobalt-doped spinel(Co²⁺:Mg Al₂O₄)is an effective way to obtain the direct output of high energy 1.5μm short pulse laser.However,the efficiency of light conversion is low and the quality of beam is relatively poor under high energy output.The key reason may be that severely Amplified Spontaneous Emission（ASE）effect in the gain medium.Therefore,it is necessary to explore a method to keep high efficiency and high beam quality laser while realizing high energy pulse laser output.In this thesis,the LD side pumped Er³⁺,Yb³⁺:glass passively Q-switched laser is studied theoretically and experimentally.The main research contents and achievements of this thesis are as follows:（1）Er³⁺,Yb³⁺:glass is determined as the working substance of laser,and its energy level characteristics are analyzed.According to the absorption characteristics of Er³⁺,Yb³⁺:glass,LD pump source with center wavelength of 940nm was adopted.Co²⁺:Mg Al₂O₄ crystal was selected as passive Q-switching element.The stability of resonant cavity was analyzed,and the parallel plane cavity was selected for experiment.The common cooling methods of solid state laser are analyzed,and the copper was selected for thermal precipitation experiment.（2）For the key problem of ASE effect,Er³⁺,Yb³⁺:glass waveguide structure was designed according to the absorption spectrum and luminescence characteristics.The waveguide structure is composed of core layer,absorption layer and pump light transmission layer.The core layer material is 1wt.%Er³⁺,21 wt.%Yb³⁺:glass,and the size is 0.8×0.8×10mm³.The four sides of Er³⁺,Yb³⁺:glass were bonded with 0.1mm Co²⁺:glass as an absorption layer to inhibit ASE formation.The material of the pump transmission layer is K9 glass,which is bonded on both sides of the waveguide to improve the pump uniformity and achieve high beam quality laser output.（3）The pump absorption efficiency and pump uniformity were simulated and analyzed in zemax non-sequence mode,and the dimension parameters of Er³⁺,Yb³⁺:glass waveguide structure were optimized based on ray tracing method.The overall length,width and thickness of the optimized waveguide structure are 10mm,8.9mm and 1mm,respectively.The pump absorption efficiency is up to 95%,and the pump uniformity is 93.7%.（4）Combined with the temperature distribution field theory,the thermal stress and thermal lens effect of Er³⁺,Yb³⁺:glass waveguide structure are theoretically analyzed and calculated,and the thermal distribution and stress distribution of waveguide are simulated in COMSOL multi-physical field simulation software to ensure the safety of waveguide structure in the experimental process.It also provides a theoretical basis for the results of subsequent bench experiments.（5）After Er³⁺,Yb³⁺:glass waveguide structure is prepared by non-adhesive bonding technology,the bench experiment is carried out.The transmittance of the output coupling mirror,the cavity length and the initial transmittance of Co²⁺:Mg Al₂O₄ crystal were optimized successively.Finally,the 1.535μm laser output with single pulse energy of 2.16m J,pulse width of 4.7ns and peak power of 459k W was achieved.The corresponding light-to-light conversion efficiency was 0.55%and the beam quality factor M² was 1.53.The optimal output laser performance of bonded Co²⁺:glass and unbonded Co²⁺:glass waveguide lasers is also compared.Compared with unbonded Co²⁺:glass waveguide lasers,the passive q-switched single pulse energy and peak power of bonded Co²⁺:glass waveguide lasers are increased by184.2%and 262%respectively.These experimental results demonstrate that the bonding of Co²⁺:glass on the four sides of Er³⁺,Yb³⁺:glass is an effective method to inhibit ASE effect and improve the output pulse energy of laser.